1. Technical Field
Example embodiments of the present invention generally relate to a high-voltage power source, a charging device incorporating that high-voltage power source, and a high-voltage power supplying method.
2. Background Art
In electrophotographic image forming apparatuses, the surface of a photoreceptor needs to be charged so as to have a desired electrical potential, for the formation of an image of good quality. In this respect, a method of applying high voltage to a charging roller that charges a photoreceptor is known. In this method, the high voltage applied to the charging roller is a voltage on which a direct-current voltage and a sinusoidal alternating-current voltage are superposed. According to this method, the electric discharge on the positive side and the electric discharge on the negative side occur in an alternate manner between the charging roller and the photoreceptor, and the surface of the photoreceptor is evenly charged so as to have a desired electrical potential.
In recent years, there are some cases in which discharging processes of a photoreceptor after the first transfer process are omitted to reduce the cost. In such cases, the photoreceptor is charged due to the first transfer bias, and the electric charge remains on the photoreceptor. Such remaining electric charge interrupts a stable discharge between the surface of the photoreceptor and the charging roller, and the surface potential of the photoreceptor deviates from a desired level. Accordingly, the quality of the formed image deteriorates.